Most economists are familiar with the late Garrett Hardin's classic article, "The Tragedy of the Commons" (see Tragedy of the Commons). Hardin's idea was that when no one owns a resource, it is overused because no one can control its usage and each person has an incentive to use it before others do. This insight has helped us understand much human behavior and has led people to advocate either having the resource privately owned or having it controlled by government.
Ostrom's work suggested, contrary to conventional thinking, that communities are able to self-organize in ways that punish those who free ride on the common resource. Examining dozens of real-world arrangements, she found instances of communal ownership that worked--that is, that did not lead to the tragic outcomes envisioned by Hardin--as well as ones that did not. Were there systematic differences? Yes, and interestingly, the ones that worked did have a kind of property rights system, just not private ownership. Based on her work, Ostrom proposed several guidelines, which the Nobel committee highlighted, for managing common-pool resources. Among them are that rules should clearly define who gets what, good conflict resolution methods should be in place, people's duty to maintain the resource should be proportional to their benefits, monitoring and punishing is done by the users or someone accountable to the users, and users are allowed to participate in setting and modifying the rules. Notice the absence of top-down government solutions.
This is from the bio of Elinor Ostrom, which has recently been posted on Econlib. As I mentioned earlier, I am writing bios of economists who have won the Nobel Prize since 2004. There are more to come.